A Navy investigation into a mass shooting at the Washington Navy Yard last year concluded that coworkers and supervisors of gunman Aaron Alexis failed to report clear signs that he was dangerously unstable.

The report concluded that The Experts, the contracting company that hired Alexis for a job at the Navy Yard, knew Alexis had been struggling with paranoia and had initiated an internal investigation into his increasingly unbalanced behavior just weeks before his Sept. 16 shooting rampage in then-Building 197, the headquarters of Naval Sea Systems Command.

The Navy concluded the shooting could have been prevented if The Experts had followed the rules for reporting signs of mental instability in contractors who hold security clearances, as Alexis did.

“Had this information been reported, properly adjudicated, and acted upon, Alexis’ authorization to access secure facilities and information would have been revoked,” said the report, signed Nov. 8 by Adm. John Richardson, who was selected to lead the Navy’s investigation into the shooting rampage that killed 12 and wounded four more before Alexis was killed by law enforcement officers.

The report details the life and death of a former sailor who had shown signs of anger and instability for years. But despite this pattern, Alexis had repeatedly escaped charges involving firearms and destructive behavior before, during and after his Navy career.

The Navy dedicated 30 investigators and 10 support personnel to dig into Alexis’ background and the events surrounding the shooting, producing a 120-page report that was released Tuesday.

A call to The Experts for comment was not immediately returned Tuesday.

History of violent tendencies

Alexis, 34 at the time of his death, graduated high school in 1999 in his native New York City. He lived there until 2001, when he moved to Seattle, and it was in Seattle that he began showing symptoms of uncontrolled anger.

In 2004, Alexis was charged after police say he shot out the back tires of a local construction worker. Alexis told police that he had shot the tires out because the man had disrespected him. The report said Alexis experienced a “blackout fueled by anger.”

The charges were dropped five days later.

Between trips to Bangkok, Thailand, in 2006 and 2007, Alexis was implicated in another incident in Bellevue, Wash. Police there say that in November 2006, Alexis was suspected of slashing the tires of five cars in the parking area of his apartment complex. All the cars belonged to Alexis’ neighbors and all had been the subject of previous complaints from Alexis.

No arrest was ever made in the incident.

During his time in Seattle, he attended DeVry University, but dropped out after less than a year. He also failed to repay the loans he took out for education, though he made periodic payments.

Troubled Navy career

Alexis joined the Navy in 2007 after moving back to New York City. Despite his arrests and several unpaid fines and tickets, Alexis lied to recruiters, saying he had “no criminal activity and no indebtedness,” the report said.

Alexis scored a 78 on his ASVAB, above average for his year, and cleared a background check for his secret clearance, despite investigators uncovering the arrest in Seattle he had failed to report.

He joined the Navy as an aviation electrician’s mate on a five-year active-duty enlistment.

In December 2007, Alexis reported to Fleet Logistics Squadron 46 in Marietta, Ga., a Reserve squadron that flew C-9 Skytrain jetliners. The investigation said Alexis had trouble adjusting to military life and that his command had attempted to mentor him. He was also ordered to attend financial counseling after further investigation turned up his undisclosed financial issues.

In 2008, Alexis had another run-in with the law after he became agitated and destructive in a Georgia night club, yelling profanities and breaking furniture.

He was arrested and charged with disorderly conduct but, again, the charges didn’t stick. He did, however, receive non-judicial punishment for being absent without leave the day after his arrest.

Alexis’ performance reports during this time ranged from “Significant Problems” to “Promotable.”

In September 2010, he was arrested again for discharging a firearm but, for a fourth time, he avoided charges and a move to administratively separate Alexis was terminated as a result. In December, Alexis applied for and was granted an early transition from the Navy and received an honorable discharge as a third class petty officer.

In March, 2011, Alexis began receiving $400 a month in disability from the VA for back and shoulder problems.

Becoming unhinged

Alexis began working for The Experts, a subcontractor working, among other places, at The Washington Navy Yard, in September 2012. During his first stint at The Experts, the report says Alexis worked at six project sites in California, Texas and Japan. He resigned in December 2012, but reapplied and was rehired in July 2013.

It was while Alexis was working projects in his latest stint that he showed signs of becoming unglued.

On August 5, his project coordinator spent 20 minutes on the phone trying to calm Alexis down, after he grew enraged that a passenger on his flight from Norfolk, Va., to Providence, R.I., was making fun of him.

The next day, he called his travel coordinator to request he be moved from the Residence Inn where he was staying because it was too noisy. Alexis relocated to Navy Gateway Inns & Suites on Naval Station Newport, R.I.

Early on the morning of Aug. 6, Alexis began showing clear signs of a man in crisis. Around 2 a.m., the police began receiving phone noise complaints from Alexis and other guests at the hotel.

Later that day, the clerk at the hotel requested a police presence in case Alexis threatened anyone, based on a call from The Experts travel coordinator concerned by Alexis’ behavior.

When police responded to the clerk’s call, they found he had taken apart his bed and was complaining about a microwave chip in his head, and that neighbors at the hotel were using a machine to keep him awake and pin him to the bed. According to the hotel’s log book, Alexis continued to cause a disturbance by banging on doors and walls complaining of noises.

The Experts’ travel coordinator met with her supervisors, who pulled Alexis off the job in Newport because of alarm at his abnormal behavior.

Before he left, however, Alexis had another run-in with Newport police. Alexis called the police claiming someone was using a microwave machine “to send vibrations through the ceiling, and that these vibrations were penetrating his body such that he could not sleep,” the report said.

The police department sent a copy of the report to Naval Station Newport with an note saying: “FYI on this. Just thought to pass it on to you in the event this person escalates.”

It was at this time that The Experts launched an internal investigation into Alexis’ behavior which turned up a history of paranoia. Alexis continued to believe that he was being targeted, telling one person on Sept. 1 that he had been under “constant bombardment from some type of [Extremely Low Frequency] weapon” that had “almost cost him his job.”

On Sept. 9, The Experts assigned Alexis to a job updating classified computers at NAVSEA headquarters on the Washington Navy Yard. On Sept. 14, he purchased a Remington-870, 12-gauge shotgun. Two days later, Alexis was dead, along with 12 other civilian contractors inside Building 197.

The shootings

Sailors assigned the Navy Yard responded heroically to the incident, the report said.

Alexis entered the Navy Yard at 7:44 a.m. on Sept. 16 with a valid common access card. He parked his car and entered Building 197 with a bag containing his sawed-off shotgun and shells.

At 8:15, he exited a fourth floor bathroom and began shooting NAVSEA employees. The first calls reporting an active shooter were made a minute later. Naval Security Forces were in the building within five minutes of the first shot being fired, according to the report. The officers went directly to the fourth floor.

At 8:37, Alexis fired his last fatal gunshot, by which time the Washington D.C. police had established a unified command at 11th and O streets.

At about 8:40, a chief hospital corpsman assigned to the Naval History and Heritage Command established a medical triage center in the parking garage across from Building 197. The chief sent a messenger to the Navy Yard clinic to get supplies and help; in about a half an hour, three medical doctors and six corpsmen were on scene.

By 9:25, Alexis was shot and killed by law enforcement officers.

By 3 p.m., Naval Security Forces had evacuated the building and Navy chaplains were notifying family members of the deceased at a command center at the Washington Nationals’ baseball stadium.

Three law enforcement officers were wounded responding to the shootings.